But what about multi key shortcuts (example Q~E), only the first key can be obtained with above code. What if I have multiple commands, all assigned multi keys (Q~A, Q~E, Q~R, ...), how to know their "full" shortcut, since the above code will only return "Q" for all of them?

for shortcut sequences you find the following keys and qualifiers with an offset of 10 in the container. So 10 and 11 for second qualifier and key, 20, 21 for third,... for up to ten keys.
Unfortunately I found this documented only in the Python docs on AddShortcut(). Sorry for the inconvenience. We'll fix the docs.

I tried to read out the container, but stopped at index 7. Should have known better to at least try until 10.
Ah, never expected the Python docs would have more info than the C++ ones. As such, I didn't think of having a look.
Thanks for pointing it out.